BASIC RESEARCH 
AT LOS ALAMOS
Los Alamos: Laboratory
(1943-1944)
Events: Bringing It All
Together, 1942-1945

The first few months at Los Alamos were occupied with briefings on nuclear physics for the technical staff and with planning research priorities and organizing the laboratory.  Leslie Groves called once again on Warren Lewis to head a committee, this time to evaluate the Los Alamos program.  The committee's recommendations resulted in the coordinated effort envisioned by those who advocated a unified laboratory for bomb research.  Enrico Fermi (right) took control of critical mass experiments and standardization of measurement techniques.  Plutonium purification work, begun at the Met Lab, became high priority at Los Alamos, and increased attention was paid to metallurgy.  The committee also recommended that an engineering division be organized to collaborate with physicists on bomb design and fabrication.  The laboratory was thus organized into four divisions: theoretical (Hans A. Bethe, right); experimental physics (Robert F. Bacher); chemistry and metallurgy (Joseph W. Kennedy); and ordnance (Navy Captain William S. "Deke" Parsons).  Like other Manhattan Project installations, Los Alamos soon began to expand beyond initial expectations.  

As director, J. Robert Oppenheimer (below) shouldered burdens both large and small, managing the numerous mundane matters such as living quarters, mail censorship, salaries, promotions, and other "quality of life" issues that were inevitable in an intellectual pressure-cooker with few social amenities.  Oppenheimer relied on a group of advisers to help him keep the "big picture" in focus, while a committee made up of Los Alamos group leaders provided day-to-day communications between divisions.  

Early experiments on both uranium and plutonium provided welcome results.  Uranium emitted neutrons in less than a billionth of a second -- just enough time, in the world of nuclear physics, for an efficient explosion.  Emilio Segrè (below) later provided an additional cushion with his discovery in December 1943 that, if cosmic rays were eliminated, the subcritical uranium masses would not have to be brought together as quickly as previously thought; nor would the uranium have to be as pure.  Muzzle velocity for the scaled-down artillery piece could be lower, and the gun could be shorter and lighter.  Segrè's tests on the first samples of plutonium demonstrated that plutonium emitted even more neutrons than uranium due to the spontaneous fission of plutoniurn-240.  Both theory and experimental data now agreed that a bomb using either element would detonate if it could be designed and fabricated into the correct size and shape.  But many details remained to be worked out, including calculations to determine how much uranium-235 or plutonium would be needed for an explosive device.  

Bacher's experimental physics division patiently generated the essential cross section measurements needed to calculate critical and efficient mass.  The same group utilized particle accelerators to produce the large numbers of neutrons needed for its cross section experiments.  Bacher's group also compiled data that helped identify tamper materials that would most effectively push neutrons back to the core and enhance the efficiency of the explosion.  Despite Los Alamos's postwar reputation as a mysterious retreat where brilliant scientists performed miracles of nuclear physics, much of the work that led to the atomic bombs was extremely tedious.  

The chemists' job was to purify the uranium-235 and plutonium, reduce them to metals, and process the tamper material.  Only highly purified uranium and plutonium would be safe from predetonation.  Fortunately, purification standards for uranium were relatively modest, and the chemical division was able to focus its effort on the lesser known plutonium and make substantial progress on a multi-step precipitation process by summer 1944.  The metallurgy division had to turn the purified uranium-235 and plutonium into metal.  Here, too, significant progress was made by summer as the metallurgists adapted a stationary-bomb technique initially developed at Iowa State College.  

Parsons (right), in charge of ordnance engineering, directed his staff to design two artillery pieces of relatively standard specifications except for their extremely light barrels -- one for a uranium bomb and one for a plutonium bomb.  The guns needed to achieve high velocities, but they would not have to be durable since they would only be fired once.  Here again early efforts centered on the more problematic plutonium weapon, which required a higher velocity due to its higher risk of predetonation.  Two plutonium guns arrived in March 1944 and were field-tested successfully.  In the same month, two uranium guns were ordered.